1. Field of the Invention
The present invention relates to an ink jet recording apparatus that discharges an ink droplet from a recording head according to recording data and records an image on a recording medium.
2. Description of the Related Art
An ink jet recording apparatus records data by discharging ink in liquid form an extremely small nozzle. When recording is not performed, moisture in the ink in the nozzle evaporates and the viscosity of the ink rises. Then, the color materials in the ink may cohere. If recording is started in such a state, the discharge performance of the recording head may be declined due to non-discharge of ink or unstable discharge of ink.
Thus, prior to recording on a recording medium, a conventional ink jet recording apparatus preliminary discharges or suctions ink which has been thickened in the nozzle due to moisture evaporation.
Further, a cap that covers the surface of the recording head is provided for the recording apparatus. The cap is helpful in preventing a discharging defect due to drying and solidifying of the ink in the nozzle that occurs when printing is not performed for a certain time. However, the cap is generally made of a material such as normal rubber, and the cap itself transmits moisture. Thus, even if the recording head is capped, if the printing is not performed for a long time, the moisture in the ink in the nozzle gradually evaporates. As a result, a preliminary discharge operation or a suction operation will be necessary before the next recording operation is started.
Additionally, the ink jet recording apparatus of recent years has used ink of multiple colors and smaller-sizes nozzles due to expansion of color gamut, improvement in gradation characteristics, and reduction in granularity. As described above, even if the recording head is capped, evaporation of the moisture or the moisture absorption of ink of each color occurs. Moisture mole fraction of ink differs according to the color of the ink. In other words, some ink dries relatively quickly but some do not. Further, the discharging defect due to moisture evaporation of ink tends to occur with fine nozzles. Thus, it is necessary to perform the preliminary discharge operation and the suction operation more frequently compared to the conventional ink jet recording apparatus.
Japanese Patent Application Laid-Open No. 2009-262353 discusses a method according to which a preliminary discharge is performed in the cap before the capping operation. Such preliminary discharge is useful to maintain the humidity in the cap nozzle for a certain period of time, so that it does not fall below a tolerable lower limit of humidity at which the possibility of discharging defect increases. Further, by performing preliminary discharge of ink with higher mole fraction of water in the cap, the timing of a next recovery operation can be delayed.
However, according to the invention discussed in Japanese Patent Application Laid-Open No. 2009-262353, since the preliminary discharge of ink with high mole fraction of water is performed in the cap before the capping operation, even if a next record command is issued shortly after the capping operation, the ink with high mole fraction of water is discharged in the cap. Thus, unnecessary ink is discharged and the amount of waste ink is increased.